Radiation therapy or radiotherapy refers to the medical use of ionizing radiation as part of cancer treatment to control malignant cells. Radiotherapy is commonly used for the treatment of malignant tumors (cancer), and may be used as the primary therapy as well as in combination with other cancer treatments. Most common cancer types can be treated with radiotherapy in some way.
Radiation therapy decreases the size of tumors and in some cases may eradicate them. Radiation can be used to shrink tumors, allowing surgical removal that would otherwise not be possible. Because tumors and their metastases can cause pain, radiating those cancerous areas may significantly reduce pain. Radiation therapy is often used for palliation (easing symptoms from incurable cancer) and pain relief when other treatments are not possible or have not been successful.
One of the major limitations of radiotherapy is that the cells of solid tumors become deficient in oxygen. This is because solid tumors usually outgrow their blood supply, causing a low-oxygen state known as hypoxia. The more hypoxic the tumors are the more resistant they are to the effects of radiation because oxygen makes the radiation damage to DNA permanent. Much research has been devoted to overcoming this problem including the use of high pressure oxygen tanks, blood substitutes that carry increased oxygen, hypoxic cell radiosensitizers such as misonidazole and metronidazole, and hypoxic cytotoxins, such as tirapazamine.
There is still, however, a need for a method and apparatus that increase effectiveness of the radiation therapy.